1. Field of the Invention
The present invention relates to a device that displays an image by modulating light from a light source through a plurality of optical modulation elements, and more particularly, to a optical display device and projection-type display device preferable for realizing enlargement of luminance dynamic range and number of gradations.
The present application claims priority on Japanese Patent Application No 2003-427208 filed on Dec. 24, 2003, Japanese Patent Application No. 2004-4025409 filed on Feb. 2, 2004, and Japanese Patent Application No. 2004-299285 filed on Oct. 13, 2004, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Dramatic improvements have been made in recent years in the image quality of liquid crystal displays (LCD), EL, plasma displays, cathode ray tubes (CRT), projectors and other optical display devices, and performance with respect to resolution and color gamut is being realized that is nearly comparable to human vision characteristics. However, the reproduction range of luminance dynamic range is at best about 1 to 102 nit, while the number of gradations is typically 8 bits. On the other hand the luminance dynamic range that can be visualized all at once by human vision is about 10−2 to 10−4 nit, while luminance disunion ability is about 0.2 nit, and when this is converted into a number of gradations, it is said to be equivalent to 12 bits When considering the displayed images of current optical display devices in terms of these vision characteristics, the narrowness of the luminance dynamic range is conspicuous, and due to a lack of gradation of shadowed and highlighted areas, displayed images appear to lack realism and impact.
In addition, in the field of computer graphics (CG) used in movies and video games, there is a growing trend to pursue greater depiction reality by giving a luminance dynamic range and number of gradations that approach human vision to display data (referred to as high dynamic range (HDR) display data). However, due to the lack of performance of optical display devices that display that data, there is the problem in which CG images are unable to adequately demons their inherent expressive capabilities.
Moreover, 16-bit color space is scheduled to be employed in next-generation operating system (OS), resulting in a dramatic increase in the luminance dynamic range and number of gradations as compared with current 8-bit color space. Consqeuently, it is desirable to realize optical display devices capable of taking advantage of 16-bit color space.
Among optical display devices, liquid crystal projectors, digital light processing (DLP, trademark of the TI Corporation) projectors and other projection-type display devices are capable of large-screen display, and are effective devices in terms of reproducing reality and impact of displayed images. In this field, the following proposals have been made to solve the aforementioned problems.
Technology for a high dynamic range projection-type display device is disclosed in, for example, Reference 1 (Japanese Unexamined Patent Application, First Publication No. 2001-100689). This display device is provided with a light source, a second optical modulation element that modulates the luminance of the the wavelength region of the light, and a first optical modulation element that modulates luminance of the wavelength region for each wavelength region of the three primary colors of red, green and blue (RGB) within the wavelength region of the light. In this device, light from the light source forms a desired luminance distribution by modulating with the second optical modulation element, the optical image is then formed on the pixel surfaces of the first optical modulation element to modulate the color, after which the secondary modulated light is projected. Each pixel of the second optical modulation element and first optical modulation element is individually controlled based on a first control value and second control value, respectively, that are detained from HDR display data. The optical modulation elements have a pixel structure or segment structure that allows independent control of the transmission factor, and transmitting modulation elements are used that are capable of controlling the two-dimensional distribution of transmission factor. A typical example of this is a liquid crystal light bulb. In addition, reflecting modulation elements way be used instead of transmitting modulation elements, and a typical example of this is a digital micromirror device (DMD).
The following considers the case of using an optical modulation element having a dark display transmission factor of 0.2% and a bright display transmission facor of 60%. In the case of the optical modulation element alone, the luminance dynamic range is 60/0.2=300. Since the aforementioned projection-type display device of the prior art is equivalent to optically arranging optical modulation elements having a luminance dynamic range of 300 in series, a luminance dynamic range of 300×300=90,000 can be realized. In addition, since the same approach is valid for the number of gradations, a number of gradations in excess of 8 bits can be obtained by optically arranging optical modulation elements having a gradation of 8 bits in series.
However, although it is necessary to increase the partition number (resolution) in the second optical modulation elements to reduce display unevenness, since a large number of optical elements are arranged between the second optical modulation element and first optical modulation element, there was the problem of it being difficult to accurately transit illumination light having a desired light intensity distribution to the first optical modulation element.
In addition, since there is considerable distance between the first and second optical modulation elements in the arrangement of first and second optical modulation elements composed by light crystal light valves, DMD and so forth, abandon of modulated light corresponding to each pixel modulated for luminance in the second optical modulation device ends up increasing in proportion to the aforementioned distance at the stage the light reaches the pixels corresponding to the first optical modulation element. Consequently, although methods have been considered in which a shift in the amount of aberration is allowed by increasing each pixel of the second optical modulation element corresponding to, for example, the aberration caused by the aforementioned distance, when this method is employed, there is the problem in which an increase in the size of the fist optical modulation element cannot be avoided. On the other hand, although a method has also been proposed that corrects the aforementioned aberration by interposing an optical element between the first and second optical modulation elements, this has the problem of resulting in increased device costs due to being unable to avoid increased complexity of the illumination optical system and the use of expensive optical elements.
In addition, since the optical length of the illumination light path of each resolved light after the light is divided into the three primary colors of red, green and blue differs from the resolved light of the other two colors with respect to resolved light of a certain single color, differences in luminance occur between the resolved light attributable to differences in optical path length. These differences in luminance cause color bleeding, color diffusion and so forth in optical images following synthesis of the resolved light.
Therefore, in focusing on the aforementioned problems of the prior art that remain unsolved, the object of the present invention is to provide an optical display device and projection-type display device that are preferable for realizing highly accurate transmission of illumination light, expansion of the luminance dynamic range and high image quality of display images while also making it possible to reduce overall device size.